The present invention relates to a variable displacement compressor comprising a refrigerant circuit of an on-vehicle air conditioner.
Generally, a compressor for an on-vehicle air conditioner has a clutch mechanism such as an electromagnetic clutch on a power transmission path between an engine, which is a drive source of the vehicle, and the compressor. When the air-conditioning is not necessary, the electromagnetic clutch is disengaged and the power is not transmitted to the compressor to stop the compressor.
However, when the electromagnetic clutch is engaged and disengaged, shock is caused, and the shock decreases the drivability of the vehicle. Therefore, recently, clutchless type compressors have been widely used. (for example, Japanese Laid-Open Patent Publication No. 7-127569) A clutchless type compressor does not have a clutch mechanism on the power transmission path between the engine and the compressor.
A variable displacement swash plate type compressor is used as a clutchless type compressor that is disclosed in the above publication. In the variable displacement swash plate type compressor, displacement can be changed based on pressure in a crank chamber, which is a swash plate accommodating chamber. In the compressor, the crank chamber and a suction chamber are connected by a bleed passage. The discharge chamber and the crank chamber are connected by a first supply passage and a second supply passage. A pressure sensitive valve is arranged in the first supply passage. The pressure sensitive valve operates by mechanically sensing the suction pressure. An electromagnetic valve is arranged in the second supply passage. The electromagnetic valve closes the second supply passage when the air-conditioning is necessary.
Therefore, when the pressure sensitive valve is operated according to changes in the suction pressure, balance is controlled between the flow rate of high pressure discharge gas introduced to the crank chamber via the first supply passage and the flow rate of gas discharged from the crank chamber via the bleed passage. The pressure in the crank chamber is thus determined.
When the air-conditioning is not necessary or the engine is running with a large load such as when the vehicle is accelerated or running at high speed, the second supply passage is opened by the electromagnetic valve. The crank chamber is maintained with high pressure regardless of the opening adjustment of the first supply passage by the pressure sensitive valve. The displacement of the compressor becomes minimum. Therefore, the compressor drive load of the engine is controlled to be minimum.
However, the bleed passage is always open in the above compressor and refrigerant gas is always introduced to the suction chamber by the bleed passage. The flow of the refrigerant gas introduced to the crank chamber by the first and the second supply passages needs to be large so that the crank chamber is maintained with high pressure to keep the minimum displacement of the compressor. Therefore, the minimum displacement of the compressor needs to be set large and the engine load necessary for driving the compressor increases. Since refrigerant gas of a large flow rate needs to be passed through the first and second supply passages, the sizes of the pressure sensitive valve and the electromagnetic valve need to be increased.
A cross-sectional area of the bleed passage may be smaller to solve the above problem. However, if the cross-sectional area of the bleed passage is small, the refrigerant gas is introduced from the crank chamber to the suction chamber slowly. The pressure of the crank chamber cannot be lowered rapidly. In other words, the displacement of the compressor cannot be increased rapidly.
Accordingly, it is an objective of the present invention to provide a displacement control device of a variable displacement compressor, which device has a small drive load at a minimum displacement and a compact valve for controlling the displacement, and also is capable of changing the compressor displacement rapidly.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a displacement control device for a variable displacement compressor in a refrigerant circuit of a vehicular air conditioner is provided. The compressor is driven by a drive source of the vehicle to compress refrigerant. The refrigerant circuit includes a low pressure zone and a high pressure zone. The low pressure zone is exposed to the pressure of refrigerant drawn into the compressor. The high pressure zone is exposed to the pressure of refrigerant compressed by the compressor. The displacement control device adjusts the pressure in a crank chamber of the compressor, thereby changing the displacement of the compressor. The control device includes a bleed passage, first and second supply passages, a first control valve, and a second control valve. The bleed passage connects the crank chamber with the low pressure zone. The first and second supply passages connect the crank chamber with the high pressure zone. The first and second supply passages are formed independent from each other. The first control valve is located in the first supply passage. The first control valve adjusts the opening size of the first supply passage and includes a pressure sensitive member and a valve body. The pressure sensitive member is displaced in response to a pressure in the refrigerant circuit. The valve body is moved by the pressure sensitive member. In response to a pressure in the refrigerant circuit, the pressure sensitive member moves the valve body such that the displacement of the compressor is changed to cancel pressure fluctuation of a pressure in the refrigerant circuit. The second control valve is located in the second supply passage and in the bleed passage. The second control valve operates in response to an external command and includes a first valve portion and a second valve portion. The first valve portion adjusts the opening size of the second supply passage, and the second valve portion adjusts the opening size of the bleed passage. When the first valve portion decreases the opening size of the second supply passage, the second valve portion increases the opening size of the bleed passage. When the first valve portion increases the opening size of the second supply passage, the second valve portion decreases the opening size of the bleed passage.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.